Representative motion information for temporal motion prediction in video encoding and decoding

ABSTRACT

Disclosed herein are representative embodiments of generating representative motion information that can be used during processing of a video frame. In one exemplary embodiment disclosed herein, a reference frame comprising a group of blocks is processed, and motion information for the group of blocks is compressed at least by buffering representative motion-vector information and representative reference-frame index information for the group of blocks. The representative reference-frame index information comprises reference-frame index information of a representative block of the group of blocks, and the representative reference-frame index information represents reference-frame index information for the group of blocks during processing of a current frame.

FIELD

The field relates to video encoding and decoding, and in particular, torepresentative motion information for use in video encoding anddecoding.

BACKGROUND

As the use of video has become more popular in today's world, video hasbecome available in a wide variety of video formats. These video formatsare provided by using traditional video coding techniques that are ableto compress video for storage and transmission, and are able todecompress video for viewing. Compression and decompression of videoconsumes computing resources and time. Although traditional video codingtechniques can be used to encode and decode video, such techniques arelimited and are often computationally inefficient.

SUMMARY

Among other innovations described herein, this disclosure presentsvarious tools and techniques for representing and using motioninformation during video encoding and/or decoding. For instance, certainembodiments of the disclosed technology store and use representativemotion information in a computationally efficient manner duringprocessing of video information, thereby saving memory resources.

In one exemplary technique described herein, a reference framecomprising a group of blocks is processed. Also, motion information forthe group of blocks is compressed at least by buffering representativemotion-vector information and representative reference-frame indexinformation for the group of blocks. The representative reference-frameindex information includes reference-frame index information of arepresentative block of the group of blocks, and the representativereference-frame index information represents reference-frame indexinformation for the group of blocks during processing of a currentframe.

In another exemplary technique described herein, at least a portion of acompressed video bitstream is received. Also, representativemotion-vector information and representative reference-frame indexinformation for a group of blocks in a reference frame is buffered. Therepresentative reference-frame index information includesreference-frame index information of a representative block of the groupof blocks. Additionally, a current frame is decoded, and therepresentative reference-frame index information includes thereference-frame index information for the group of blocks that isbuffered in the buffer during the decoding of the current frame.Further, decoded video information for the current frame is stored.

This summary is provided to introduce a selection of concepts in asimplified form that are further described below. This summary is notintended to identify key features or essential features of the claimedsubject matter, nor is it intended to be used to limit the scope of theclaimed subject matter. The foregoing and other objects, features, andadvantages of the technologies will become more apparent from thefollowing detailed description, which proceeds with reference to theaccompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a generalized example of a suitablevideo encoder system for use with certain disclosed embodiments.

FIG. 2 is a schematic diagram of a generalized example of a suitablevideo decoder system for use with certain disclosed embodiments.

FIG. 3 is a flowchart of an exemplary method of compressing motioninformation.

FIG. 4 is a schematic diagram of a decoder storing compressed motioninformation for a group of blocks.

FIG. 5 is a flowchart of an exemplary method of decoding a compressedvideo bitstream.

FIG. 6 is a schematic diagram illustrating using representative motioninformation for a group of blocks.

FIG. 7 is a schematic diagram of an exemplary decoder capable ofdecoding video information.

FIG. 8 is a flowchart of an exemplary method of decoding videoinformation.

FIG. 9 is a schematic diagram illustrating selection of a representativeblock for a group of blocks according to an embodiment of the disclosedtechnology.

FIG. 10 is a schematic diagram illustrating selection of arepresentative block for a group of blocks by scanning according to anembodiment of the disclosed technology.

FIG. 11 is a schematic diagram illustrating a generalized example of asuitable computing environment for any of the disclosed embodiments.

DETAILED DESCRIPTION I. General Considerations

Disclosed below are representative embodiments of methods, apparatus,and systems for determining and using representative motion informationduring video encoding and/or decoding. The disclosed methods, apparatus,and systems should not be construed as limiting in any way. Instead, thepresent disclosure is directed toward all novel and nonobvious featuresand aspects of the various disclosed embodiments, alone and in variouscombinations and sub-combinations with one another. Furthermore, anyfeatures or aspects of the disclosed embodiments can be used alone or invarious combinations and sub-combinations with one another. Thedisclosed methods, apparatus, and systems are not limited to anyspecific aspect or feature or combination thereof, nor do the disclosedembodiments require that any one or more specific advantages be presentor problems be solved

Although the operations of some of the disclosed methods are describedin a particular, sequential order for convenient presentation, it shouldbe understood that this manner of description encompasses rearrangement,unless a particular ordering is required by specific language set forthbelow. For example, operations described sequentially may in some casesbe rearranged or performed concurrently. Moreover, for the sake ofsimplicity, the attached figures may not show the various ways in whichthe disclosed methods, apparatus, and systems can be used in conjunctionwith other methods, apparatus, and systems. Furthermore, as used herein,the term “and/or” means any one item or combination of items in thephrase.

II. Exemplary Encoders and Decoders

A. Overview

FIG. 1 is a schematic diagram of a generalized video encoder system 100,and FIG. 2 is a schematic diagram of a video decoder system 200, inconjunction with which various described embodiments may be implemented.

The relationships shown between modules within the encoder and decoderindicate the flow of information in the encoder and decoder; otherrelationships are not shown for the sake of simplicity. In particular,FIGS. 1 and 2 usually do not show side information indicating theencoder settings, modes, tables, etc. used for a video sequence, frame,macro-block, slice, block, etc. Such side information is sent in theoutput bitstream, typically after entropy encoding of the sideinformation. The format of the output bitstream can be theHigh-Efficiency Video Coding (HEVC) format or another video codingformat.

Depending on the implementation and the type of compression desired,modules of the encoder or decoder can be added, omitted, split intomultiple modules, combined with other modules, and/or replaced with likemodules. In alternative embodiments, encoders or decoders with differentmodules and/or other configurations of modules perform one or more ofthe described techniques.

B. Exemplary Video Encoder

FIG. 1 is a schematic diagram of a generalized video encoder system 100that can store and use representative motion information as describedbelow. The encoder system 100 receives a sequence of video framesincluding a current frame 105, and produces compressed video information195 as output. For example, the compressed video information can be acompressed video bitstream, and a video frame can be a picture in thesequence of pictures in the video. Particular embodiments of videoencoders can use a variation or supplemented version of the generalizedencoder 100.

The encoder system 100 can compress frames of a video sequence (e.g.,predicted frames and key frames). For the sake of presentation, FIG. 1shows a path for encoding blocks of a frame using inter-predictionthrough the encoder system 100 (shown as the inter-coded blocks path)and a path for encoded blocks of a frame using intra-prediction (shownas the intra-coded blocks path). Many of the components of the encodersystem 100 can be used for compressing both inter-predicted andintra-predicted blocks. In the illustrated embodiments, components thatcan be shared are labeled with the same number, though it is to beunderstood that each path can be implemented using separate dedicatedcomponents as well. The exact operations performed by those componentscan vary depending on the type of information being compressed.

An inter-coded block is represented in terms of prediction (ordifference) from one or more other blocks. A prediction residual is thedifference between what was predicted and the original block. Incontrast, an intra-coded block is compressed without reference to otherframes. When encoding a block, the encoder system 100 can choose toencode the block using an inter-prediction mode and/or anintra-prediction mode.

If a current block 105 is to be coded using inter-prediction, a motionestimator 110 estimates motion of the current block 105, or sets ofpixels of the current block 105 with respect to a reference frame usingmotion information, where the reference frame is a previouslyreconstructed frame 125 buffered in the store 120. The motioninformation for the reference frame can also be buffered. In someimplementations, motion information is buffered as representative motioninformation. In alternative embodiments, the reference frame is atemporally later frame or the current block is bi-directionallypredicted. The motion estimator 110 outputs as side information motioninformation 115, such as motion vectors, inter-prediction directions,and/or reference frame indices. A motion compensator 130 applies themotion information 115 to the reconstructed previous decoded frame (thereference frame) 125 to form a motion-compensated current block 135. Theprediction is rarely perfect, however, and the difference between themotion-compensated current block 135 and the original current block 105is the prediction residual 145. Alternatively, a motion estimator andmotion compensator apply another type of motion estimation/compensation.

If the current block 105 is to be coded using intra-prediction, anintra-predictor 155 creates an intra-predicted current block prediction140 from stored pixels of the frame that includes the current block 105,and the stored pixels are previously reconstructed pixels buffered inthe store 120. The intra-predictor 155 can output side information suchas intra-prediction direction 158. The prediction is rarely perfect,however, and the difference between the stored pixels and the originalcurrent block 105 is the prediction residual 185.

A frequency transformer 160 converts the spatial domain videoinformation into frequency domain (e.g., spectral) data using afrequency transform. A quantizer 170 then quantizes the blocks ofspectral data coefficients.

When a reconstructed current block or frame is needed for subsequentmotion estimation/compensation and/or intra-prediction, an inversequantizer 176 performs inverse quantization on the quantized spectraldata coefficients. An inverse frequency transformer 166 then performsthe inverse of the operations of the frequency transformer 160,producing a reconstructed residual (for a predicted frame) or areconstructed key frame. If the current block 105 was coded usinginter-prediction, the reconstructed prediction residual is added to themotion-compensated current block 135 to form the reconstructed currentblock. If the current block 105 was coded using intra-prediction, thereconstructed prediction residual is added to the intra-predictedcurrent block prediction 140 to form the reconstructed current block.The store 120 can buffer the reconstructed current block for use inpredicting subsequent frames or blocks.

The entropy coder 180 compresses the output of the quantizer 170 as wellas certain side information (e.g., motion information 115, modes,quantization step size). Typical entropy coding techniques includearithmetic coding, variable length coding, differential coding, Huffmancoding, run length coding, LZ coding, dictionary coding, andcombinations of the above.

The entropy coder 180 stores compressed video information 195 in thebuffer 190. The compressed video information 195 is depleted from thebuffer 190 at a constant or relatively constant bit rate and stored forsubsequent streaming at that bit rate. Alternatively, the encoder system100 streams compressed video information immediately followingcompression.

The encoder 100 can produce a bitstream, perform motion vectorprediction, and store and use representative motion information asdescribed below. The encoder may also use the techniques describedherein in various combinations, individually, or in conjunction withother techniques. Alternatively, another encoder or tool performs one ormore encoding techniques.

C. Exemplary Video Decoder

FIG. 2 is a schematic diagram of a general video decoder system 200 thatcan store and use representative motion information as described below.The decoder system 200 receives information 295 for a compressedsequence of video frames (e.g., via a compressed video bitstream) andproduces output including a reconstructed block 205. Particularembodiments of video decoders can use a variation or supplementedversion of the generalized decoder 200.

The decoder system 200 decompresses blocks coded using inter-predictionand intra-prediction. For the sake of presentation, FIG. 2 shows a pathfor intra-coded blocks through the decoder system 200 (shown as theintra block path) and a path for inter-coded blocks (shown as the interblock path). Many of the components of the decoder system 200 are usedfor decompressing both inter-coded and intra-coded blocks. The exactoperations performed by those components can vary depending on the typeof information being decompressed.

A buffer 290 receives the information 295 for the compressed videosequence and makes the received information available to the entropydecoder 280. The buffer 290 typically receives the information at a ratethat is fairly constant over time. The buffer 290 can include a playbackbuffer and other buffers as well. Alternatively, the buffer 290 receivesinformation at a varying rate.

The entropy decoder 280 entropy decodes entropy-coded quantized data aswell as entropy-coded side information (e.g., motion information 215,flags, modes, and other side information), typically applying theinverse of the entropy encoding performed in the encoder. An inversequantizer 270 inverse quantizes entropy-decoded data. An inversefrequency transformer 260 converts the quantized, frequency domain datainto spatial domain video information by applying an inverse transformsuch as an inverse frequency transform.

If the block 205 to be reconstructed is an inter-coded block usingforward-prediction, a motion compensator 230 applies motion information215 to a reference frame 225 to form a prediction 235 of the block 205being reconstructed. A buffer (store) 220 stores previous reconstructedframes for use as reference frames. Also, motion information for thereconstructed frames can be stored, and the stored motion informationcan include representative motion information. Alternatively, a motioncompensator applies other types of motion compensation. The predictionby the motion compensator is rarely perfect, so the decoder 200 alsoreconstructs a prediction residual 245 to be added to the prediction 235to reconstruct block 205.

When the decoder needs a reconstructed frame for subsequent motioncompensation, the frame store 220 buffers the reconstructed frame foruse in predicting a subsequent frame. In some implementations ofpredicting a frame, the frame is predicted on a block-by-block basis (asillustrated) and respective blocks of the frame can be predicted. One ormore of the predicted blocks can be predicted using motion informationfrom blocks in the same frame or one or more blocks of a differentframe.

If the block 205 to be reconstructed is an intra-coded block, anintra-predictor 255 forms a prediction 265 of the block 210 beingreconstructed. The buffer (store) 220 stores previous reconstructedblocks and frames. The prediction by the motion compensator is rarelyperfect, so the decoder 200 also reconstructs a prediction residual 275to be added to the prediction 265 to reconstruct block 210.

The decoder 200 can decode a compressed bitstream, perform motion vectorprediction, and store and use representative motion information asdescribed below. The decoder may also use the techniques describedherein in various combinations, individually, or in conjunction withother techniques. Alternatively, another decoder or tool performs one ormore decoding techniques.

II. Exemplary Embodiments of Storing and Using Motion Information

A. Exemplary Method of Compressing Motion Information

Motion information coding comprises a large portion of the totalbit-rate in video coding, and efficient motion information coding canimprove coding performance Motion information can include one or moremotion vectors, one or more reference-frame indices, and one or morecoding modes. In some video coding designs, temporal motion information(e.g., motion information from other frames) is used to predict themotion information of a frame being currently decoded which can improvecoding performance. During processing of video (e.g., during encoding ordecoding of video information), one or more buffers can be maintained tostore motion information for reference frames to be available for use inthe processing of other frames.

FIG. 3 is a flowchart of an exemplary method 300 of compressing motioninformation. In the illustrated example, a reference frame that includesa group of blocks is processed at block 310. For example, the processingof the reference frame can include determining motion information forone or more blocks of the group of blocks that is encoded or decodedusing inter prediction, and/or determining that one or more of theblocks of the group of blocks are intra-prediction mode blocks. At block320, the motion information for the group of blocks is compressed atleast by buffering representative motion-vector information andrepresentative reference-frame index information and/or the modeinformation for the group of blocks. In one implementation, theselection of buffered reference-frame index information and/orcoding-mode information matches the selection of the referencemotion-vector information. For example, the motion-vector informationand reference-frame index information of a single representative blockof the group of blocks is buffered to be available for use as substituteor representative motion information for any of the blocks of the groupof blocks during processing of subsequent frames. Also, the motioninformation for blocks in the group of blocks other than therepresentative block is discarded and not buffered in a buffer to beavailable for use during subsequent processing of other frames. That isto say, the motion information for one block that includes motion-vectorinformation, reference-frame index information, and coding-modeinformation can be stored and used as a substituted or representativemotion information for a whole group of blocks. A block can be a groupof samples or pixels in a frame (e.g., a 4×4 block, an 8×8 block, a16×16 block, and other such block arrangements). By using motionvectors, reference-frame indexes, and coding modes associated with asingle block, the storing of mismatched motion information can beavoided. In one implementation the compressed motion information isstored before storing, in the buffer, the frame where the compressedmotion information was derived from. In other implementations, thecompressed motion information can be stored at some other time duringthe video decoding or encoding processes.

Compressing the motion information for a group of blocks can reduce thememory requirement for storing (e.g., buffering) the motion informationfor the group of blocks by reducing the number of motion vectors,reference frame indexes, and modes to be stored for the group of blocks.In one particular exemplary implementation, the representativereference-frame index information is the only reference-frame indexinformation for the group of blocks that is buffered in the bufferduring the processing of a current frame, and the representativereference motion-vector information is the only motion-vectorinformation for the group of blocks that is buffered in the bufferduring the processing of a current frame. For example, during processing(e.g., encoding or decoding) of a current frame, the reference-frameindex information is stored in a buffer to represent the reference-frameindex information for each of the blocks in the group of blocks. In someimplementations, representative coding-mode information is also bufferedfor the group of blocks. For example, in one particular exemplaryimplementation, the representative coding-mode information is the onlycoding-mode information for the group of blocks that is buffered in thebuffer during the processing of a current frame.

In other implementations, a current block is processed in part by usingrepresentative reference-frame index information from a block in thegroup of blocks other than the representative block and/or a currentblock is processed in part by using representative coding-modeinformation from a block in the group of blocks other than therepresentative block. In yet another implementation, a block in thegroup of blocks that has an available motion vector is selected as therepresentative block for the group of blocks.

B. Exemplary System for Using Motion Information

FIG. 4 is a schematic diagram illustrating a decoder 400 that includes abuffer 410 storing compressed motion information 420 for a group ofblocks in a reference frame. The motion information includesrepresentative reference-frame index information 430 and representativemotion-vector information 440. Also, in the example, the compressedmotion information includes representative coding-mode information 450.In the illustrated embodiment, the representative coding-modeinformation 450 is also consistent with the representativereference-frame index information 430 and representative motion-vectorinformation 450 such that it is from the same block of the group ofblocks. Coding-mode information for a block can indicate a coding modefor the block. The coding mode can then be used to determine if a motionvector is or is not available (e.g., the motion vector exists or isstored) for the block. In one implementation, one of the availablecoding modes is an inter-prediction mode, which indicates that the blockis coded using inter prediction (e.g., between frame/pictureprediction). A block indicating that it is coded using inter-predictioncoding can be decoded using one or more reference frames and usingmotion information, including one or more motion vectors andreference-frame indices. The one or more motion vectors andreference-frame indices used to decode the block in an inter-predictionmode can be included in the motion information for the block (e.g.,representative index information 430, representative motion vectorinformation 440). Another possible coding mode indicated by thecoding-mode information is an intra-prediction mode, which indicatesthat the block is coded using intra prediction (e.g., within aframe/picture prediction). A block indicating that it is coded usingintra-prediction coding can be decoded using information from the framewithout using a motion vector, reference-frame index, or another frame.A block decoded using intra-prediction (e.g., a block ofintra-prediction mode) does not have one or more motion vectors and/orreference-frame indices for the block. That is to say, no motion vectorsor reference indices are used to decode the intra-prediction mode block.

C. Exemplary Method of Decoding a Compressed Video Bitstream

FIG. 5 is a flowchart of an exemplary method 500 of decoding acompressed video bitstream. In the exemplary method, at least a portionof a compressed video bitstream is received at 510. For example, thecompressed video bitstream can be encoded according to a video codingformat such as HEVC or some other video coding format. In oneimplementation, one or more coded frames are included in the compressedvideo bitstream. At 520, representative motion-vector information andrepresentative reference-frame index information for a group of blocksin a reference frame is buffered after the reference frame is decoded.For example, the representative motion-vector information andrepresentative reference-frame index information can be consistent suchthat they are from the same block (e.g., a representative block) in thereference frame. The reference frame can be a video frame decoded fromthe compressed video bitstream. In certain implementations, thereference frame contains samples or blocks that can be used for interprediction decoding of samples or blocks in another frame (e.g., acurrently decoded frame), or the reference frame contains representativemotion-vector information and representative reference-frame indexinformation. The reference frame index can reference which otherreference frame to use when multiple reference frames are available. Forexample, a reference-frame index can be an index into a list ofreference frames (e.g., a reference frame list) that references aparticular reference frame in the list of reference frames. In oneimplementation, the reference-frame index is used to reference areference frame that is used with a motion vector to locate a block orother group of samples or pixels in the reference frame. The referenceframe list is a list of reference frames that can be used in interprediction of another frame (e.g., a P or B frame) or slice. Forexample, the slice can be a group of a number (e.g., an integer number)of blocks in a frame ordered consecutively according to a raster scan.In some implementations, there can be one reference frame list foruni-prediction of a P slice and two reference frame lists forbi-prediction of a B slice.

With reference to FIG. 5 , at block 530, a current frame is decoded. Incertain implementations, during the decoding, the reference-frame indexinformation buffered in the buffer for the group of blocks is used asthe representative reference-frame index information. For example, thebuffered reference-frame index information can be used asreference-frame index information for a co-located block in thereference frame that is co-located with the current block in the currentframe. In some implementations, the co-located block is a differentblock than the representative block. Further, in particularimplementations, the reference-frame index information comprises asingle reference-frame index for the group of blocks and is from arepresentative block. For example, a current block in the current framecan be decoded using a reference frame, and the reference frame caninclude a group of blocks that includes a block co-located with thecurrent block. The group of blocks can further include representativereference-frame index information from a representative block in thegroup of blocks that is used as the reference-frame index informationfor the entire group of blocks. Accordingly, during the decoding of thecurrent block, the representative reference-frame index information forthe group of blocks is used as reference-frame index information for aco-located block in the reference frame that is co-located with thecurrent block in the current frame. For example, during motion vectorprediction for a current block in a current frame, when motioninformation for the co-located block in the reference frame is to beused, the stored representative motion information (e.g., the motioninformation of the representative block) is substituted and actuallyused. In some implementations of motion vector prediction, motioninformation from a previously decoded block (e.g., a block in the sameframe or different frame) is used to predict the motion information fora unit (e.g., block, slice, or other unit) in a current frame. Forexample, temporal motion vector prediction (TMVP) uses motioninformation from a unit (e.g., a block) in a reference frame (e.g., apreviously decoded frame) to predict the motion information for a unitin a current frame. Further, when a temporal motion vector is used todetermine a prediction for a block, the motion vector for a co-locatedblock in a reference frame different than the current frame can be usedas the temporal motion vector. In some implementations, the co-locatedblock in the reference frame is co-located with the unit in the currentframe. For instance, the co-located block can be a block in a referenceframe that has an upper-left corner or upper-left pixel or sample withthe same spatial coordinates of an upper-left corner or upper-left pixelof a current block in a current frame. In some implementations, theco-located block can be a different sized block than the block in thecurrent frame with which it is co-located. For example, the co-locatedblock in the reference frame can be a 4×4 block and the block in thecurrent frame that it is co-located with can be a block of a differentsize (e.g., a block having more or less pixels or samples). In additionto square blocks, which have the same amount of horizontal pixels asvertical pixels, blocks can be rectangular. A rectangular block can havemore or less horizontal pixels than vertical pixels (e.g., 16×32, 32×16,16×8, 8×16, or other sizes). In a further implementation, duringdecoding, the motion information of the representative block can be usedto determine a prediction for the current block. The prediction can bean estimate of sample values or data elements of the block currentlybeing decoded.

At block 540, decoded video information for the current frame is stored.For example, the decoded frame is stored in a decoded picture buffer orsome other store.

FIG. 6 is a schematic diagram that illustrates using representativemotion information 600 for a group of blocks 605 in a reference frame610 during motion vector prediction for a current frame 615. Storingmotion information and reference frame information during encoding anddecoding can consume a large amount of memory resources. For example aunit can be a 4×4 pixel block, such as block 620. To store such a 4×4block in a buffer costs 24 bytes for a 4:2:0 format when the pixels are1.5 bytes or 12 bpp. For a P-frame there can be one motion vector for ablock, and for a B-frame there can be two motion vectors for a block. Amotion vector includes two components which include a horizontaldisplacement component and a vertical displacement component. Therefore,for one 4×4 block in a B-frame, when an integer is stored using 2 bytes,it will cost 8 bytes of memory to save the motion vector, which is ⅓ thestorage cost of the pixels of the 4×4 block at 24 bytes. Additionalmemory is consumed by storing the coding-mode information andreference-frame index information for the block. By compressing motioninformation, the memory requirement for buffering the motion informationfor a group of blocks can be reduced. In compressing motion information,some motion vectors for a group of blocks are discarded and not storedin memory during subsequent encoding/decoding of other frames to reducethe memory requirement for storing the motion information for the groupof blocks.

With reference to FIG. 6 , the group of blocks 605 is a macro-block thatis a 16×16 pixel block that includes 16 4×4 sub-blocks 620-635. Duringencoding or decoding, instead of buffering motion vectors for each ofthe 4×4 sub-blocks within the group of blocks 605 in buffer 650, onlythe motion information of one of the sub-blocks in the group of blocks605, such as representative block 635 or other representative block ofthe group of blocks 605, is stored as representative motion information600. In the illustrated embodiment, the representative block 635 is thelast block in the group of blocks 605 (e.g., the lowermost and rightmostblock in the group of blocks 605). The motion information of therepresentative block 635 is stored as representative motion informationand later used as motion information for any of the sub-blocks of thegroup of blocks 605 during subsequent processing of frames. That is tosay that only the motion information for the representative block 635 isstored to represent the motion information for all of the 4×4 pixelsub-blocks within the 16×16 pixel macro-block. For a 16×16 macro-blocksuch as the group of blocks 605, by compressing motion information, thememory requirement for storing motion information for the group ofblocks can be reduced to 1/16^(th) the memory requirement of storing themotion information for each of the sub-blocks of the group of blocks605. For example, if all of the 16 sub-blocks are inter-prediction modeblocks in a P-frame, storing motion information for each of the 16sub-blocks consumes memory resources to hold 16 motion vectors, 16reference indices, and 16 coding modes. Storing compressed motioninformation for this group of blocks consumes an amount of memoryresources that holds motion information for one of the blocks whichincludes 1 motion vector, 1 reference-frame index, and 1 coding mode. Inother implementations, not all blocks of a group of blocks have motionvectors and/or reference-frame indices and compressing the motioninformation for the group of blocks produces a same or different (e.g.,higher or lower) memory saving ratio.

When motion information for any of the particular blocks (e.g., any ofthe respective blocks of the group of blocks) in the group of blocks 605is needed for use or used during subsequent encoding or decoding, thestored representative motion information 600 (the representative motioninformation from the representative block, such as the last block in thegroup of blocks 605 (e.g., the lowermost and rightmost block 635 in thegroup of blocks 605)) is used instead. That is to say, once therepresentative motion information 600 is buffered, processing ofsubsequent frames can use the representative motion information 600 asmotion information for any of the 16 blocks of the group of blocks 605.For example, during decoding for the current block 645 in the currentframe 615 (e.g., during temporal motion vector prediction or some otherdecoding process), motion information of a co-located block such asblock 630 in the group of blocks 605 can be requested for use in thedecoding. Because block 630 is co-located with current block 645 themotion information for block 630 is requested for use, but instead therepresentative motion information 600 is used as the motion informationfor block 630 in the decoding of the current block 645. In the exampleof FIG. 6 , the buffered representative information 600 includes amotion vector, a reference-frame index, and a coding mode that are themotion information for the representative block 635. In otherimplementations, the representative motion information 600 of therepresentative block can be different or the same as the motioninformation of the representative block 635 (e.g., the motioninformation can be from any one of blocks 620-635).

D. Exemplary System for Decoding a Current Frame of Video

FIG. 7 is a schematic diagram of an exemplary decoder 700 capable ofdecoding a current frame of video. The decoder 700 includes one or moreprocessing units 705 and a memory 710. The one or more processing unitsare at least configured to decode video information. In the decoding,the decoder 700 receives at least a portion of a compressed videobitstream 715 at 720. Also, representative motion-vector information 730and representative reference-frame index information 735 for a group ofblocks in a decoded reference frame is buffered in buffer 740. Therepresentative reference-frame index information 735 includesreference-frame index information of a representative block of the groupof blocks in the reference frame. Additionally, at 750, a current frameis decoded by the decoder 700 and the representative reference-frameindex information is the only reference-frame index information for thegroup of blocks that is buffered during the decoding of the currentframe. In some implementations, representative coding-mode informationfor the group of blocks in the decoded reference frame is buffered inbuffer 740.

E. Exemplary Method of Decoding a Compressed Video Bitstream

FIG. 8 is a flowchart of an exemplary method 800 of decoding a currentframe of video. In the illustrated example, a block with an availablemotion vector is selected as a representative block for a group ofblocks in a previously decoded reference frame at block 810. Forexample, any block of the group of blocks that has an available motionvector can be selected as the representative block. In someimplementations the selection can be a default selection where apredetermined block is selected as the representative block. Forexample, the first block of the group of blocks can be the defaultselection for the representative block. In another example, the lastblock of the group of blocks can be a default selection for therepresentative block. In other implementations, respective other blocksin the group of blocks are the default selection for the representativeblock.

In some implementations, the representative block is selected byscanning or searching the group of blocks for a block with an availablemotion vector. For example, the group of blocks can be scanned in apredetermined or fixed order. In some implementations, the scanning ofthe blocks continues until a block is scanned which has an availablemotion vector. For example, the first block scanned with an availablemotion vector is selected. In another implementation, the scanning canbegin from the first block, the last block, or some other block. Forexample, the blocks can be scanned from the first block toward the lastblock, or scanned from the last block toward the first block. In someimplementations, each block scanned is adjacent to the previouslyscanned block. In another implementation, if a predetermined or defaultblock is to be selected as the representative block, but thepredetermined block does not have an available motion vector (e.g., theblock is coded using intra prediction), the rest of the blocks can bescanned to find a block that has available motion information for motionvector prediction. In another implementation, the blocks are scanned byscanning one block per coding mode region of the group of blocks. Forexample, a coding mode region of the group of blocks can be a sub-groupof blocks (e.g., 4 4×4 blocks that comprise a 8×8 block or some othersub-group of blocks) that have the same coding mode. In oneimplementation, a coding mode region that includes a block ofintra-prediction mode indicates that the blocks of the mode region arepredicted using intra prediction and do not have associated motionvectors, or reference indices that can be used for prediction of anotherblock's motion vector or motion vectors. Scanning one block of a codingmode region of intra-prediction mode blocks is sufficient to indicatethat no available motion vector can be found in the mode region, and theother blocks of the coding mode region can be skipped by the scanning.In one example, a mode region that includes a block of inter-predictionmode indicates that the blocks of the mode region are predicted usinginter prediction, so by scanning one block of the mode region issufficient to find a block with an available motion vector for motionvector prediction.

With reference to FIG. 8 , at block 820, representative motion-vectorinformation for a group of blocks in the decoded reference frame isbuffered. In particular implementations, the representativemotion-vector information for the group of blocks can be themotion-vector information for the last block in the group of blocks(e.g., the lowermost and rightmost block in the group of blocks). Atblock 830, representative reference-frame index information for a groupof blocks in the decoded reference frame is buffered. In particularimplementations, the representative reference-frame index informationfor the group of blocks can be the reference-frame index information forthe last block in the group of blocks (e.g., the lowermost and rightmostblock in the group of blocks). At block 840, representative coding-modeinformation for the group of blocks in the decoded reference frame isbuffered. In particular implementations, the representative coding-modeinformation for the group of blocks can be the coding-mode informationfor the last block in the group of blocks (e.g., the lowermost andrightmost block in the group of blocks). At block 850, a current frameis decoded at least in part by using the representative reference-frameindex information as reference-frame index information for a co-locatedblock in the decoded reference frame. In some implementations, thedecoding of frames can be in a different order than the received orderor display order of the frames of the video. In another implementationthe representative block is a different block than the co-located blockin the reference frame. At block 860, the current frame is decoded atleast in part by using the representative coding-mode information ascoding-mode information for the co-located block in the decodedreference frame. For example, the coding-mode information can be checkedor used during temporal motion vector prediction to determine if thereis available motion information for the group of blocks (e.g., thecoding mode is checked to determine if the coding mode indicates aninter-prediction mode or intra-prediction mode). The current frame canalso be decoded at least in part by using the representativemotion-vector information as motion-vector information for theco-located block in the decoded reference frame as shown at block 870.

FIG. 9 is a schematic diagram that illustrates the process of selectinga representative block for a group of blocks 910. In the figure, thegroup of blocks 910 is a 16×16 pixel macro block comprised of 16 4×4pixel sub-blocks 920-935. The group of blocks 910 is organized incolumns and rows. In the illustration of the group of blocks 910, eachsmall box illustrates a 4×4 pixel block. In some implementations, theordering of the blocks can be in a raster scan order. For example, thefirst block such as block 920 can be the leftmost block in the firstrow, and the last block such as block 935 can be the rightmost block inthe last row.

Block 935 is predicted using inter prediction and has availablemotion-vector information, reference-frame index information, andcoding-mode information that can be used for motion vector prediction ofanother block in a current frame, such as current block 940. When thespatial position of a representative block is closer to the centroid ofa current block in a current frame, the prediction for the current blockcan be better. By choosing the last 4×4 block as the representativeblock of a 16×6 pixel macro-block comprised of 4×4 pixel blocks, therepresentative block can provide a better prediction for a current blockthat is larger than a 16×16 pixel block. For example, the last block 935in the group of blocks 910 is spatially closer, in its frame, to thelocation of the centroid of the current block 940 than is the firstblock 920 in the group of blocks. The current block 940 in the currentframe is a 32×16 pixel block that is co-located with the first block920. As co-located frames, the upper left corners of the first block 920and the current block 940 have the same spatial position in theirrespective frames which is represented by the illustrated arc 945. Inanother example, by choosing the last 4×4 pixel block in a 16×16 pixelblock as the representative block, the spatial position of therepresentative block is also closer than the first block to the centroidfor a current frame that is a 16×32 pixel block which is co-located withthe first block in the reference frame. When a video coding format(e.g., HEVC or other video coding format) uses many large size blocks,choosing the last block of a group of blocks to be the representativeblock for compressed motion information for motion vector prediction canbe better than choosing the first block of the group of blocks as therepresentative block.

FIG. 10 is a schematic diagram that illustrates selecting arepresentative block for a group of blocks 1005 by scanning. In theexample, the group of blocks 1005 is a 16×16 pixel block comprising 164×4 pixel blocks 1010-1025. In other implementations, a group of blockscan be different sizes. The blocks 1010-1019 and blocks 1022-1023 arepredicted using inter prediction (e.g., blocks of inter-prediction mode)and have motion-vector information that can be used in motion vectorprediction (e.g., temporal motion vector prediction) for another blockin a different frame. In the illustrated embodiment, the blocks1020-1021 and blocks 1024-1025 are predicted using intra prediction(e.g., blocks of intra-prediction mode) and do not have associatedmotion-vector information (e.g., one or more motion vectors) that can beused in motion vector prediction (e.g., temporal motion vectorprediction) for another block in a different frame. In one example, amotion vector can be a two-dimensional value, having a horizontalcomponent that indicates left or right special displacement and avertical component that indicates up or down spatial displacement.

To select a representative block for the group of blocks 1005, theblocks are scanned. During the scanning the scanned blocks are checkedto determine if there is motion information available (e.g., there is amotion vector stored or otherwise available, or the block is ofinter-prediction mode) for the block. If there is motion-vectorinformation available for a scanned block the block can be chosen as arepresentative block. If none of the blocks have valid (e.g., available)motion information, then a predetermined motion vector (e.g., a (0, 0)motion vector or some other motion vector) can be stored to representthe motion information for the group of blocks. In the example of FIG.10 , the blocks are scanned starting from the last block which is block1025, and are scanned toward the first block which is block 1010. Thegroup of blocks is scanned by regions of blocks having like modes. Inother implementations, the group of blocks are scanned consecutively ina raster scan order or in the reverse of a raster scan order from astarting block toward another block, and the scanning ends when a blockis found (e.g., the first block found) that has an available motionvector that can be selected as a representative block. Scanningconsecutively can be either in an ascending order or descending order.That is to say the blocks can be scanned either forward or backwards.

In FIG. 10 , the regions of blocks having alike coding modes are moderegions 1030, 1040, 1050, 1060. The respective blocks that comprise themode regions 1030, 1040, 1050, and 1060 are indicated in FIG. 10 asbeing within the solid lines and connected by dotted lines. For example,the dotted lines of region 1030 are between the connected blocks 1010,1011, 1014, and 1015. In the example of FIG. 10 , the scanning of thegroup of blocks starts at block 1025 which is the last block of thegroup. Block 1025 is an intra-prediction mode block and therefore has novalid motion vector. As block 1025 has no valid motion vector, thescanning skips over the other blocks of mode region 1060 and continuesto the first block in the next mode region in the consecutive orderingof the blocks from the last block toward the first block to scan block1023. Block 1023 is an inter-prediction mode block and has a validmotion vector, so the scanning ends and block 1023 is selected as therepresentative block for the group of blocks 1005. In otherimplementations, the scanning continues to find a different block withan available motion vector. For example, if block 1023 did not have anavailable motion vector, one block (e.g., only one block) per moderegion can be scanned until a scanned block is found that has a validmotion vector.

III. Exemplary Computing Environment

FIG. 11 illustrates a generalized example of a suitable computingenvironment 1100 in which herein described embodiments, techniques,solutions, and technologies may be implemented. The computingenvironment 1100 is not intended to suggest any limitation as to scopeof use or functionality of the technology, as the technology may beimplemented in diverse general-purpose or special-purpose computingenvironments. For example, the disclosed technology may be implementedusing one or more computing devices comprising a processing unit,memory, and storage storing computer-executable instructionsimplementing the technologies described herein. For example, computingdevices include server computers, desktop computers, laptop computers,notebook computers, netbooks, tablet computers, mobile devices, PDAdevices and other types of computing devices (e.g., devices such astelevisions, media players, or other types of entertainment devices thatcomprise computing capabilities such as audio/video streamingcapabilities and/or network access capabilities). The disclosedtechnology may also be implemented with other computer systemconfigurations, including hand held devices, multiprocessor systems,microprocessor-based or programmable consumer electronics, network PCs,minicomputers, mainframe computers, a collection of client/serversystems, or the like. The disclosed technology may also be practiced indistributed computing environments where tasks are performed by remoteprocessing devices that are linked through a communications network. Ina distributed computing environment, program modules may be located inboth local and remote memory storage devices. Additionally, thetechniques, technologies, and solutions described herein can beperformed in a cloud computing environment (e.g., comprising virtualmachines and underlying infrastructure resources).

With reference to FIG. 11 , the computing environment 1100 includes atleast one central processing unit 1110 and memory 1120. In FIG. 11 ,this basic configuration 1130 is included within a dashed line. Thecentral processing unit 1110 executes computer-executable instructions.In a multi-processing system, multiple processing units executecomputer-executable instructions to increase processing power and assuch, multiple processors can be running simultaneously. The memory 1120may be volatile memory (e.g., registers, cache, RAM), non-volatilememory (e.g., ROM, EEPROM, flash memory, etc.), or some combination ofthe two. The memory 1120 stores software 1180 that can, for example,implement one or more of the technologies described herein. A computingenvironment may have additional features. For example, the computingenvironment 1100 includes storage 1140, one or more input devices 1150,one or more output devices 1160, and one or more communicationconnections 1170. An interconnection mechanism (not shown) such as abus, a controller, or a network, interconnects the components of thecomputing environment 1100. Typically, operating system software (notshown) provides an operating environment for other software executing inthe computing environment 1100, and coordinates activities of thecomponents of the computing environment 1100.

The storage 1140 may be removable or non-removable, and includesmagnetic disks, magnetic tapes or cassettes, CD-ROMs, CD-RWs, DVDs, orany other tangible storage medium which can be used to store informationand which can be accessed within the computing environment 1100. Thestorage 1140 stores computer-executable instructions for the software1180, which can implement technologies described herein.

The input device(s) 1150 may be a touch input device, such as akeyboard, keypad, mouse, touch screen, controller, pen, or trackball, avoice input device, a scanning device, or another device, that providesinput to the computing environment 1100. For audio, the input device(s)1150 may be a sound card or similar device that accepts audio input inanalog or digital form, or a CD-ROM reader that provides audio samplesto the computing environment 1100. The output device(s) 1160 may be adisplay, printer, speaker, CD-writer, DVD-writer, or another device thatprovides output from the computing environment 1100.

The communication connection(s) 1170 enable communication over acommunication medium (e.g., a connecting network) to another computingentity. The communication medium conveys information such ascomputer-executable instructions, compressed graphics information,compressed or uncompressed video information, or other data in amodulated data signal.

IV. Further Considerations

Any of the disclosed methods can be implemented as computer-executableinstructions stored on one or more computer-readable media (tangiblecomputer-readable storage media, such as one or more optical mediadiscs, volatile memory components (such as DRAM or SRAM), or nonvolatilememory components (such as hard drives)) and executed on a computingdevice (e.g., any commercially available computer, including smartphones or other mobile devices that include computing hardware). By wayof example, computer-readable media include memory 1120 and/or storage1140. As should be readily understood, the term computer-readable mediadoes not include communication connections (e.g., 1170) such asmodulated data signals.

Any of the computer-executable instructions for implementing thedisclosed techniques as well as any data created and used duringimplementation of the disclosed embodiments can be stored on one or morecomputer-readable media. The computer-executable instructions can bepart of, for example, a dedicated software application or a softwareapplication that is accessed or downloaded via a web browser or othersoftware application (such as a remote computing application). Suchsoftware can be executed, for example, on a single local computer (e.g.,any suitable commercially available computer) or in a networkenvironment (e.g., via the Internet, a wide-area network, a local-areanetwork, a client-server network (such as a cloud computing network), orother such network) using one or more network computers.

For clarity, only certain selected aspects of the software-basedimplementations are described. Other details that are well known in theart are omitted. For example, it should be understood that the disclosedtechnology is not limited to any specific computer language or program.For instance, the disclosed technology can be implemented by softwarewritten in C++, Java, Perl, JavaScript, Adobe Flash, or any othersuitable programming language. Likewise, the disclosed technology is notlimited to a particular type of hardware. Certain details of suitablecomputers and hardware are well known and need not be set forth indetail in this disclosure.

Furthermore, any of the software-based embodiments (comprising, forexample, computer-executable instructions for causing a computing deviceto perform any of the disclosed methods) can be uploaded, downloaded, orremotely accessed through a suitable communication means. Such suitablecommunication means include, for example, the Internet, the World WideWeb, an intranet, software applications, cable (including fiber opticcable), magnetic communications, electromagnetic communications(including RF, microwave, and infrared communications), electroniccommunications, or other such communication means.

The disclosed methods can also be implemented by specialized computinghardware that is configured to perform any of the disclosed methods. Forexample, the disclosed methods can be implemented (entirely or at leastin part) by an integrated circuit (e.g., an application specificintegrated circuit (“ASIC”) or programmable logic device (“PLD”), suchas a field programmable gate array (“FPGA”)).

In view of the many possible embodiments to which the principles of thedisclosed invention may be applied, it should be recognized that theillustrated embodiments are only preferred examples of the invention andshould not be taken as limiting the scope of the invention. Rather, thescope of the invention is defined by the following claims and theirequivalents. We therefore claim as our invention all that comes withinthe scope and spirit of these claims and their equivalents.

1.-20. (canceled)
 21. One or more non-transitory computer-readable mediahaving stored thereon computer-executable instructions for causing oneor more processing units, when programmed thereby, to perform operationsof a video encoder, the operations comprising: encoding a first frame ofa video sequence, thereby producing a first portion of encoded data;reconstructing the first frame; buffering, in memory, the first framefor use as a reference frame; buffering, in memory, representativemotion vector information and representative reference frame indexinformation for the reference frame, including buffering representativemotion vector information and representative reference frame indexinformation for a group of blocks in the reference frame, wherein therepresentative reference frame index information for the group of blocksis reference frame index information of a representative block of thegroup of blocks, and wherein the representative motion vectorinformation for the group of blocks is a motion vector of therepresentative block of the group of blocks; encoding a second frame ofthe video sequence, thereby producing a second portion of the encodeddata, including using the motion vector and the reference frame indexinformation of the representative block of the group of blocks to encodea block of the second frame; and outputting the encoded data.
 22. Theone or more computer-readable media of claim 21, wherein the block ofthe second frame has a co-located block in the reference frame, andwherein the co-located block in the reference frame is a different blockthan the representative block of the group of blocks.
 23. The one ormore computer-readable media of claim 22, wherein the co-located blockin the reference frame and the representative block of the group ofblocks have different sizes.
 24. The one or more computer-readable mediaof claim 22, wherein the co-located block in the reference frame and therepresentative block of the group of blocks have different top-leftcorner positions in the reference frame.
 25. The one or morecomputer-readable media of claim 21, wherein the operations furthercomprise: buffering, in memory, representative coding mode informationfor the reference frame, including buffering representative coding modeinformation for the group of blocks in the reference frame, wherein therepresentative coding mode information for the group of blocks is codingmode information of the representative block of the group of blocks. 26.The one or more computer-readable media of claim 25, wherein the codingmode information of the representative block of the group of blocksindicates whether the representative block of the group of blocks wasencoded using intra prediction or inter prediction.
 27. One or morenon-transitory computer-readable media having stored thereoncomputer-executable instructions for causing one or more processingunits, when programmed thereby, to perform operations of a videodecoder, the operations comprising: receiving encoded data in abitstream for at least part of a video sequence; decoding a first frameof the video sequence using a first portion of the encoded data;buffering, in memory, the first frame for use as a reference frame;buffering, in memory, representative motion vector information andrepresentative reference frame index information for the referenceframe, including buffering representative motion vector information andrepresentative reference frame index information for a group of blocksin the reference frame, wherein the representative reference frame indexinformation for the group of blocks is reference frame index informationof a representative block of the group of blocks, and wherein therepresentative motion vector information for the group of blocks is amotion vector of the representative block of the group of blocks; anddecoding a second frame of the video sequence using a second portion ofthe encoded data, including using the motion vector and the referenceframe index information of the representative block of the group ofblocks to reconstruct a block of the second frame.
 28. The one or morecomputer-readable media of claim 27, wherein the motion vector of therepresentative block of the group of blocks is the only motion vectorinformation buffered for the group of blocks during the decoding thesecond frame, and wherein the reference frame index information of therepresentative block of the group of blocks is the only representativereference frame index information buffered for the group of blocksduring the decoding the second frame.
 29. The one or morecomputer-readable media of claim 27, wherein the block of the secondframe has a co-located block in the reference frame, and wherein theco-located block in the reference frame is a different block than therepresentative block of the group of blocks.
 30. The one or morecomputer-readable media of claim 29, wherein the co-located block in thereference frame and the representative block of the group of blocks havedifferent sizes.
 31. The one or more computer-readable media of claim29, wherein the co-located block in the reference frame and therepresentative block of the group of blocks have different top-leftcorner positions in the reference frame.
 32. The one or morecomputer-readable media of claim 27, wherein the operations furthercomprise: buffering, in memory, representative coding mode informationfor the reference frame, including buffering representative coding modeinformation for the group of blocks, wherein the representative codingmode information for the group of blocks is coding mode information ofthe representative block of the group of blocks.
 33. The one or morecomputer-readable media of claim 32, wherein the decoding the secondframe further includes using the coding mode information of therepresentative block of the group of blocks to reconstruct the block ofthe second frame.
 34. The one or more computer-readable media of claim32, wherein the coding mode information of the representative block ofthe group of blocks indicates whether the representative block of thegroup of blocks was encoded using intra prediction or inter prediction.35. The one or more computer-readable media of claim 27, wherein theusing the motion vector to reconstruct the block of the second frameincludes using the motion vector to determine a temporal motion vectorprediction for the block of the second frame.
 36. The one or morecomputer-readable media of claim 27, wherein the operations furthercomprise: selecting a rightmost block in a last row of the group ofblocks or a leftmost block in a first row of the group of blocks as therepresentative block of the group of blocks.
 37. The one or morecomputer-readable media of claim 27, wherein the representative motionvector information and the representative reference frame indexinformation for the reference frame are buffered for 16×16 blocks in thereference frame.
 38. The one or more computer-readable media of claim27, wherein the representative reference frame index information of therepresentative block of the group of blocks is an index in a list ofreference frames.
 39. One or more non-transitory computer-readable mediahaving stored thereon encoded data in a bitstream for at least part of avideo sequence, the encoded data having been encoded, with a computersystem that implements a video encoder, by operations comprising:encoding a first frame of a video sequence, thereby producing a firstportion of encoded data; reconstructing the first frame; buffering, inmemory, the first frame for use as a reference frame; buffering, inmemory, representative motion vector information and representativereference frame index information for the reference frame, includingbuffering representative motion vector information and representativereference frame index information for a group of blocks in the referenceframe, wherein the representative reference frame index information forthe group of blocks is reference frame index information of arepresentative block of the group of blocks, and wherein therepresentative motion vector information for the group of blocks is amotion vector of the representative block of the group of blocks; andencoding a second frame of the video sequence, thereby producing asecond portion of the encoded data, including using the motion vectorand the reference frame index information of the representative block ofthe group of blocks to encode a block of the second frame.
 40. The oneor more computer-readable media of claim 39, wherein the block of thesecond frame has a co-located block in the reference frame, and whereinthe co-located block in the reference frame is a different block thanthe representative block of the group of blocks.